1. Field of the Invention
The present invention relates to a display device, and more particularly to a flat panel display device that is adaptive for improving picture quality by use of a repair process and a compensation circuit and a fabricating method thereof, and a picture quality controlling method and apparatus thereof.
2. Discussion of the Related Art
Recently, the use of various flat panel display devices having reduced weight and size compared to cathode rate tube devices, has been on the rise. Flat panel display devices include liquid crystal displays, field emission displays, plasma display panels, and displays employing organic light emitting diodes.
Flat panel display devices include a display panel for displaying a picture and testing processes are used to identify panel defects in the display panel. The panel defects can include defects caused by the difference in the number of lens in an exposure machine and bright spots caused by defective pixels. These panel defects can cause brightness differences on a display screen. In other words, when applying data signals of the same gray level value to each of a panel area having a panel defect and a panel area not having a panel defect, the image displayed in the area having a panel defect can be darker or brighter than the picture displayed in the defect free area, or colors viewed in the defect area and the defect free area may appear to be different. The panel defects are primarily generated in a fabrication process, and may have a fixed form such as dot, line, belt, circle, polygon, or may have one of various other forms related to the cause of panel defect generation. Panel defects of various forms are shown in FIGS. 1A to 1E. Panel defects in the form of vertical belts as shown in FIGS. 1A to 1C result primarily from overlapping exposures and a difference in the number of lenses, while panel defects having a dot shape, as shown in FIG. 1D are primarily the result of impurities. The panel defects might result in a defective product depending on the severity and number of the panel defects, and accordingly panel defects may reduce product yield resulting in increased product cost. Further, even when a unit having a panel defect can be shipped as a good product, the deterioration in picture quality due to the panel defect reduces the reliability of the product. Accordingly, various methods have been proposed in order to reduce the occurrence of the panel defects. The improvement methods of the related art are mainly related to solving problems in the fabrication process, but there is a limit to the amount of reduction of panel effects that can be achieved using the fabrication process solutions of the related art.
A defective pixel appearing as a panel defect of a dot shape may be generated by problems such as impurities present in the fabrication process. The presence of these impurities may cause patterning defects resulting in a short or open of a signal line, a defect in a thin film transistor (hereinafter, referred to as “TFT”), or a defect in an electrode pattern. Picture quality defects caused by the defective pixels may appear as either a dark spot or bright spot on the display screen. Because a bright spot is more readily perceived by the naked eye than a dark spot, for a defective pixel appearing as a bright spot a repair process is used to make the defective pixel appear as a dark spot to reduce the deteriorating effect of the defective pixel on the picture quality. However, while a defective pixel appearing as a dark spot, as shown in FIG. 2A, may be nearly imperceptible on a display screen displaying a the black gray level, a defective pixel on an area of a display screen displaying a medium gray level or a white gray level, as shown in FIGS. 2B and 2C, is clearly perceptible as a dark spot in the middle gray level and in the bright gray level area of the display.
In addition to the problems related to panel defects, a bright line effect associated with the backlight may adversely affect picture quality. The bright line effect is a picture quality defect associated with liquid crystal display devices that employing a backlight, and is generated by a non uniform intensity of the light emitted by the backlight.
FIG. 3 illustrates an example of the bright line effect primarily associated with liquid crystal display devices using a direct type backlight. Backlights of the related art structural improvements to address the bright line problem of the backlight. However, the backlight structures of the related art do not completely address the problem of bright line effects associated with the backlight.